LONDON (Reuters) - A new vaccine against hepatitis C has shown promising results in an early-stage clinical trial, British and Italian scientists said on Wednesday.

They said the experimental vaccine, which is based on a modified cold virus and was safety-tested in 41 people, generated immune responses similar to those seen in people who have a rare but natural defense against the disease.

The results suggest it might be possible in the future to develop a potentially long-lasting hepatitis C vaccine that would be broadly effective.

But the researchers, whose findings were published in Science Translational Medicine today, cautioned that much more research is needed over many years before a successful vaccine could be fully developed.

"We've found that it's possible to prime large cellular immune responses against hepatitis C that last for at least a year," said Paul Klenerman of Britain's Oxford University, who led the first trials of the vaccine in humans.

"The immune responses we've seen are exciting and we are beginning the next stage of trials," he said in a statement about the results, adding: "It could be a long road."

Because hepatitis C is a virus that constantly changes, it is a tricky target for designing a vaccine. There are also six different strains of the virus, making it difficult to make vaccine that works for all types.

The team worked with researchers from Britain's Birmingham University and from Okairos, a small Italian biotech firm, on a new approach to developing a vaccine by stimulating a different part of the immune system from those tried before.

The new vaccine, the researchers explained, is designed to generate a response in the immune system's T-cells to the internal parts of the virus, which are more constant, rather than trying to prime an antibody attack on the virus's ever-changing outer coat.

"The outside shell of the hepatitis C virus is very variable but the inside of the virus is much more stable. That's where the engine of the virus is, where we may be able to successfully target many of the crucial pieces of machinery," said Klenerman.

The team tested the vaccine in a phase I study designed primarily to gauge the vaccine's safety. A total of 41 healthy adults took part in the study and results showed the vaccine appeared safe and was able to stimulate a large T-cell response against hepatitis C that lasted for at least a year.

The Oxford researchers are starting trials to see if the vaccine can help treat people already infected with hepatitis C, as well as continuing to develop the vaccine to get better immune responses.

"T-cell responses often become weak in those with chronic hepatitis C infections," Klenerman said. "It may be that using a vaccine to boost their immunity could become part of any treatment with other drugs."

A separate research team in the United States is also planning a larger trial in at-risk groups to see if the vaccine can protect against hepatitis C infection, he said.